A method for planarizing the surface of a semiconductor wafer or device during manufacture. Dependencies of polish rate and substrate thickness on process parameters of downforce and polish speed, and on the characteristic product high feature area on the wafer, are explicitly defined and used to control Chemical-Mechanical Polish in Run-to-Run and real-time semiconductor production control applications.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for determining critical polish time t c using a polish pad during semiconductor manufacture of a structure having one or more mesas and one or more valleys, comprising the steps of: obtaining the value of mask-scale or reticle mask-scale M; determining a pad compression spring constant k of the polish pad; measuring on a patterned structure high feature and low feature thicknesses at one or more identifiable locations, the first such measurement (before any polish) determining the values of y m0 (high features) and y v0 (low features); determining the polish recipe value for downforce F dn pushing the structure against the polish pad; determining the planar structure polish rate R p ; and computing a critical polish time prior to encountering one of the valleys according to: t c = F d n - M k A w ( y m o - y v o ) k A w R p . [ M1 ]
2. The method according to claim 1 wherein: for time t≦t c , the removal rate on mesas R m and mesa thickness y m are given as R m = R p M [M 2] y m = y mo + R p t M . [M 3]
4. The method of claim 1 wherein the step of obtaining the value of mask-scale or reticle mask-scale M comprises obtaining the value from a photomask manufacturer for a given structure's photomask.
7. The method of claim 1 wherein the step of obtaining the value of mask-scale or reticle mask-scale M comprises calculating M as a weighted average of a mask-scale or reticle mask-scale M aid a local M.
9. The method according to claim 1 wherein: R p = - CS F dn A w [M 10] where C=Preston's coefficient S=pad-to-structure speed.
10. The method according to claim 1 , further comprising the step of determining the planar structure polish rate R p , comprising the additional steps of: a. measuring the substrate film thickness at one or more identifiable locations on a planar (unpatterned) structure; b. polishing the structure for a metered amount of time; c. re-measuring the substrate film thickness at the same locations as in Step a, above; and d. differencing the measurements (Step c measurements minus Step a measurements), averaging the results, and dividing by the polish time to calculate R p , the planar structure polish rate.
11. The method according to claim 10 , further comprising the step of determining the polish pad compression spring constant k, comprising the additional steps of: e. measuring high feature and low feature thicknesses at one or more identifiable locations on the structure, the first such measurement (before any polishing) determining the values of y m0 (high features) and y v0 (low features); f. subsequently measuring after the first post-polish measurements to determine the values of y m (high features) and y v (low features); g. polishing the set of patterned structures sequentially with incremental polish times, the increments being typically 5 to 30 seconds, using an increment in polish time such that the incremental polish time multiplied by the number of structures in the set equals or exceeds the polish time normally used for the given set of patterned structures; h. re-measuring high feature and low feature thicknesses on each structure at the same locations as Step e, above; i. identifying the critical polish time as the polish time of the first structure in the sequence of increasing polish times that exhibits low feature thickness loss, and identifying the critical height h c by the high and low feature thickness difference for this first structure; j. repeating Steps e through i as needed to improve resolution (polishing with times in the vicinity of the last result in Step i) and to replicate results; and k. using the resulting values of t c and h c in Equation M1 to solve for k.
12. The method according to claim 10 , further comprising the step of determining the polish pad compression spring constant k, comprising the additional steps of: e. measuring high feature and low feature thicknesses at one or more identifiable locations on a patterned structure, the first such measurement (before any polishing) determining the values of y m0 (high features) and y v0 (low features); f. subsequently measuring after the first post-polish measurements to determine the values of y m (high features) and y v (low features); g. polishing the patterned structure for a short (typically 5 to 30 seconds) metered amount of time; h. re-measuring high feature and low feature thickness at the same locations as Step e; i. repeating Steps g and h, until low feature thickness loss is noted; j. obtaining cumulative polish time by summing the time of each polish of Step g for providing an estimate for t c and high minus low feature thickness for providing an estimate for h c ; k. repeating Steps e through j to improve resolution (polish with times in the vicinity of the result in Step j) and replicate results as needed; and l. when an adequately repeatable and accurate result for t c and h c is obtained, use Equation M1 to solve for k given the values of t c and h c .
14. The method according to claim 13 wherein the step of determining the planar wafer polish rate R p comprises the steps of: l. measuring the substrate film thickness at one or more identifiable locations on a planar (unpatterned) wafer; m. polishing the wafer for a metered amount of time; n. re-measuring the substrate film thickness at the same locations as in Step 1, above; and o. differencing the measurements (Step n measurements minus Step 1 measurements), averaging the results, and dividing by the polish time to calculate R p , the planar wafer polish rate.
17. The method according to claim 13 wherein Step h comprises filtering selected from among the group consisting of Kalman or EWMA filters.
18. The method according to claim 17 wherein EWMA filtering is used: R p ,new_estimate=λ*( R p ,new_value)+(1−λ)*R p ,old_estimate where the EWMA filter constant k has a value between 0 and 1.
19. The method according to claim 13 , further comprising the step of: l. for the next wafer or batch of wafers, repeating the sequence of steps starting with Step b.
21. The method according to claim 20 wherein Step b comprises implicit solution performed by minimization of a quadratic objective function Φ by: minimizing Φ over the allowed range of the planar polish rate R p where Φ={ y m −( y v0 +h c +R p ( t−t c )+(1 −M ) h c [exp( kR p A w ( t−t c )/ F dn )−1)} 2 wherein the vector of measurements of y m by the in-situ substrate thickness sensor are used in this manner to create an optimal value for R p .
23. The method according to claim 20 , further comprising the step of: f. creating an alarm if resulting R p values determined in Step c are outside normal expectations.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
March 28, 2003
April 26, 2005
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